Abstract: :
Purpose: PAX2, a member of the paired homeobox transcriptionfactor family, is expressed in the early optic cup, optic stalk,otic vesicle, neural tube, and urogenital system. While studiesfrom other labs have indicated that PAX2 may be involved inproliferation and/or survival in kidney cells (Dressler et al.,1993), the only evidence to support such a role for PAX2 inthe nervous system are observations by Favor et al., (1996)and Green et al (1997), in which it was noted that a loss ofPAX2 leads to retinal and neural tube hypoplasia. This studyaddresses the hypothesis that PAX2 is critical for ventral opticcup precursors to remain undifferentiated to aid in the proliferationand migration of cells that give rise to the ventral optic cup.Methods: A bicistronic vector that expresses either green fluorescent(GFP) alone or in addition to PAX2 was electroporated in ovointo optic cup precursors during early optic cup developmentat Hamburger and Hamilton stage 18–20 (E3). Sections andwholemounts expressing control and PAX2 were analyzed usingmorphometry, immunocytochemistry and in situ hybridization onE4, E6, and E8. Proliferation was studied by studies using tritiatedthymidine and/or BrDU uptake. Identification of proliferatingcells was analyzed using a BrDU–specific antibody and/orautoradiography on cytospun samples from labeled retinae. Results:Control embryos electroporated with GFP alone appeared to becompletely normal on the electroporated and control sides, whereasembryos that were electroporated with PAX2 showed phenotypesthat appeared to vary with the region of retina that was electroporated.Preliminary evidence indicates those that were electroporatednear the dorsal margin of the optic cup developed a small globeof neuroepithelial cells resembling a secondary neural retina,while expression of PAX2 in the ventral portion of the opticcup led to formation of colobomas and larger than normal opticstalks. There did not appear to be an increase in proliferationor a change in survival of cells in regions expressing PAX2.Conclusions: The effects of ectopic PAX2 expression in the developingoptic cup were hemi–retina–dependent. None of theeffects appeared to be dependent upon increased proliferationand/or survival in the nervous system.